One commonly used system for communicating a multiplicity of telephonic messages includes multiplexing techniques wherein samples of a plurality of telephone circuits are rapidly sampled with the samples being interleaved in time sequence in a well-known fashion which permits these samples to be demultiplexed whereupon the original telephonic messages can be recovered. The multiplexed messages are often transmitted by a wireless transmission link at a suitable carrier frequency such as an X-band carrier frequency.
A problem arises in that it is frequently desirable to inject an additional data channel into the communication link at a point removed from the location of the aforesaid multiplexing and for removing this additional data at a point distant from the location of the aforesaid demultiplexing. Such a data channel is frequently referred to as a service channel and serves the function of allowing operators of the telephone equipment to communicate with each other without interfering with the multiplexed telephonic messages.